High frequency dielectric ceramic composition, dielectric resonator, dielectric filter, dielectric duplexer, and communication device

ABSTRACT

A high frequency dielectric ceramic composition includes: as a major component a composition which contains a rare earth element (Re), Al, Sr, and Ti as metal elements and has a composition formula expressed by a molar ratio of aRe 2 O 3 —bAl 2 O 3 —cSrO—dTiO 2  in which a, b, c, and d satisfy the following formula; 0.113≦a≦0.172, 0.111≦b≦0.171, 0.322≦c≦0.388, 0.323≦d≦0.396, and a+b+c+d=1.000; and 0.01 to 2 parts by weight on a Fe 2 O 3  conversion basis of Fe as an element, based on 100 parts by weight of the major component.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a high frequency dielectricceramic composition for use in a high frequency region such as microwaveand millimeter-wave regions, a dielectric resonator, a dielectricfilter, a dielectric duplexer, and a communication device each using thehigh frequency dielectric ceramic composition.

[0003] 2. Description of the Related Art

[0004] Heretofore, dielectric ceramics have been widely used fordielectric resonators, circuit substrate materials, and so forth whichoperate in a high frequency region such as microwave and millimeter-waveregions.

[0005] The dielectric characteristics required for the high frequencydielectric ceramics are as follows. (1) The wavelength of anelectromagnetic wave is reduced to 1/(εr)^(1/2) in a dielectric.Accordingly, to meet requests for the reduction in size of the ceramics,it is required for the dielectric constants (E;) to be large. (2) Thedielectric losses should be low, i.e., the Q values should be high. (3)The stability of the resonance frequencies for temperature should behigh, i.e., the temperature coefficients (T_(f)) of the resonancefrequencies should be near 0 (ppm/° C.).

[0006] Heretofore, as the above-described dielectric ceramics,Re₂O₃—Al₂O₃—SrO—TiO₂ (Re: rare earth element) type materials, and thematerials containing Mn added thereto are disclosed, e.g., in JapaneseUnexamined Patent Application Publication No. 11-71171 and JapaneseUnexamined Patent Application Publication No. 2000-203934.

[0007] The Re₂O₃—Al₂O₃—SrO—TiO₂ type materials of the related art aresuperior in that the dielectric constants (ε_(r)) are high, the Q valuesare high, and the temperature coefficient (T_(f)) of the resonancefrequency can be controlled to be near zero. However, with recentadvancement of the communication enterprises, high frequency electronicparts have been required to have higher qualities. Moreover, materialsfor dielectric ceramics have been required to have a higher Q value thanthe related art materials.

SUMMARY OF THE INVENTION

[0008] Accordingly, it is an object of the present invention to providea high frequency dielectric ceramic composition which has a higher Qvalue than the related art Re₂O₃—Al₂O₃—SrO—TiO₂ type material, and havesuch a high dielectric constant (ε_(r)) as that of the related artRe₂O₃—Al₂O₃—SrO—TiO₂ type material and a small temperature coefficient(τ_(f)) of the resonance frequency, and to provide a dielectricresonator, a dielectric filter, a dielectric duplexer, and acommunication device each using the high frequency dielectric ceramiccomposition.

[0009] According to the present invention, there is provided a highfrequency dielectric ceramic composition which comprises: a majorcomponent, a composition of which contains a rare earth element (Re),Al, Sr, and Ti as metal elements, wherein a composition formulaexpressed by a molar ratio of aRe₂O₃—bAl₂O₃—cSrO—dTiO₂ in which a, b, c,and d satisfy the following formula; 0.113≦a≦0.172, 0.111≦b≦0.171,0.322≦c≦0.388, 0.323≦d≦0.396, and a+b+c+d=1.000; and a sub-component,which 0.01 to 2 parts by weight of Fe as an element on the basis of aFe₂O₃, with respect to 100 parts by weight of the major component.

[0010] Preferably, the rare earth element (Re) comprises La, or La andat least one of the other rare earth elements.

[0011] Preferably, there is provided a dielectric resonator including adielectric ceramic, wherein the dielectric ceramic is made of theabove-described high frequency dielectric ceramic composition.

[0012] Preferably, there is provided a dielectric filter which comprisesthe above-described dielectric resonator and an external coupling means.

[0013] Preferably, there is provided a dielectric duplexer whichcomprises at least two dielectric filters, input-output connecting meansconnected to the dielectric filters, respectively, and anantenna-connecting means connected to both of the dielectric filters, atleast one of the dielectric filters being the above-described dielectricfilter.

[0014] Preferably, there is provided a communication device whichcomprises the above-described dielectric duplexer, a transmissioncircuit connected to at least one of the input-output connecting meansfor the dielectric duplexers, a reception circuit connected to at leastone of the input-output connecting means which is different from theabove-described input-output connecting means to which the transmissioncircuit is connected, and an antenna connected to the antenna-connectingmeans for the dielectric duplexer.

[0015] The high frequency dielectric ceramic composition has a high Qvalue compared to the related art Re₂O₃—Al₂O₃—SrO—TiO₂ type material,and a high dielectric constant (ε_(r)) and a small temperaturecoefficient (If) of the resonance frequency which are on the same levelof those of the related art Re₂O₃—Al₂O₃—SrO—TiO₂ type material.

[0016] Thus, the dielectric resonator, the dielectric filter, thedielectric duplexer, and the communication device, which are formed ofthe above-described high frequency dielectric ceramic composition, havesuperior characteristics, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a cross-sectional view of a TE01δ mode dielectricresonator which is an example of the dielectric resonator of the presentinvention;

[0018]FIG. 2 is a perspective view of a TEM mode dielectric resonatorwhich is another example of the dielectric resonator of the presentinvention;

[0019]FIG. 3 is a cross-sectional view taken along plane a-b of thedielectric resonator shown in FIG. 2; and

[0020]FIG. 4 is a block diagram of an example of the communicationdevice of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021]FIG. 1 is a cross-sectional view of a TE01δ mode dielectricresonator 11 which is an example of the dielectric resonator of thepresent invention. Referring to FIG. 1, a dielectric resonator 11 isprovided with a metallic case 12. A columnar dielectric ceramic 14,supported by a support 13, is arranged in the space within the metalliccase 12. A coupling loop 15 is formed between the core conductor of acoaxial cable 17 and the outer conductor thereof, which functions as aninput terminal. Moreover, a coupling loop 16 is formed between the coreconductor of a coaxial cable 18 and the outer conductor thereof, whichfunctions as an output terminal. Each terminal is supported by themetallic case 12 with each outer conductor being electrically connectedto the metallic case 12. The dielectric ceramic 14 is electromagneticfield coupled with the input and output terminals to be operated. Only asignal having a predetermined frequency, input via the input terminal,is output via the output terminal. The dielectric ceramic 14 provided inthe dielectric resonator 11 is formed of the high frequency dielectricceramic composition of the present invention.

[0022]FIG. 2 is a perspective view of a TEM mode dielectric resonatorwhich is another example of the dielectric resonator of the presentinvention. FIG. 3 is a cross-sectional view taken along plane a-b of adielectric resonator 21 shown in FIG. 2. Referring to FIGS. 2 and 3, thedielectric resonator 21 comprises a prism-shaped dielectric ceramic 22having a through-hole. An inner conductor 23 a is formed in thethrough-hole. An outer conductor 23 b is formed in the periphery of theceramic 22. The Input-output terminals, i.e., external coupling meansare electromagnetic field coupled with the dielectric ceramic 22 to beoperated as a dielectric resonator. The dielectric ceramic 22constituting the dielectric resonator 21 is formed of the high frequencydielectric ceramic composition of the present invention.

[0023]FIG. 1 shows an example of the TE01δ mode dielectric resonator,and FIG. 2 shows an example of the prism-shaped TEM mode dielectricresonator, as described above. These dielectric resonators are notrestrictive. The high frequency dielectric ceramic composition of thepresent invention may be also used for dielectric resonators havingother shapes and other TEM modes, TE modes and TM modes.

[0024]FIG. 4 is a block diagram of an example of the communicationdevice of the present invention. The communication device 30 comprises adielectric duplexer 32, a transmission circuit 34, a reception circuit36, and an antenna 38. The transmission circuit 34 is electricallyconnected to an output-connecting means 40 of the dielectric duplexer32. The reception circuit 36 is connected to an output-connecting means42 of the dielectric duplexer 32. The reception circuit 36 is connectedto an output-connecting means 42 of the dielectric duplexer 32. Theantenna 38 is connected to an antenna-connecting means 44 of thedielectric duplexer 32. The dielectric duplexer 32 contains twodielectric filters 46 and 48. Each of the dielectric filters 46 and 48comprises the dielectric resonator of the present invention having anexternal-coupling means connected thereto. For example, each of thedielectric filters 46 and 48 comprises external-coupling means 50connected to the input-output terminals of the dielectric resonator 11shown in FIG. 1. One dielectric filter 46 is connected between theinput-connecting means 40 and the other dielectric filter 48. The otherdielectric filter 48 is connected between the one dielectric filter 46and the output-connecting means 42.

[0025] The high frequency dielectric ceramic composition of the presentinvention contains as a major component a composition containing asmetal elements a rare earth element (Re), Al, Sr, and Ti, having acomposition formula by a molar ratio of aRe₂O₃—bAl₂O₃—cSrO—dTiO₂ inwhich a, b, c, and d satisfy formulae of 0.113≦a≦0.172, 0.111≦b≦0.171,0.322≦c≦0.388, 0.323≦d≦0.396, and a++b+c+d=1.000. The ceramiccomposition contains 0.01 to 2 parts by weight, on a Fe₂O₃ conversionbasis, of Fe as an element, based on 100 parts by weight of the majorcomponent.

[0026] By employing the above-defined composition range, the highfrequency dielectric ceramic composition can be provided which has ahigher Q value than the related art Re₂O₃—Al₂P₃—SrO—TiO₂ type material,such a high dielectric constant (6 r) as the related artRe₂O₃—Al₂P₃—SrO—TiO₂ type material, and a small temperature coefficient(τ^(f)) of the resonance frequency.

EXAMPLES

[0027] Hereinafter, the present invention will be described withreference of more specific examples.

Example 1

[0028] As starting materials, powders of La₂O₃ which is a rare earthoxide (Re₂O₃), aluminum oxide (Al₂O₃), strontium carbonate (SrCO₃), andtitanium oxide (TiO₂) each having a high purity were prepared.

[0029] These raw materials were mixed so as to obtain compositionshaving a composition formula of aRe₂O₃—bAl₂O₃—cSrO—dTiO₂ in which thecoefficients (molar ratio) a, b, c, and d are indicated in Tables 2 and3. TABLE 1 Q × f Fe2O3 value- La2O3 Al2O3 SrO TiO2 (parts by Q × fincreasing τf Sample a b c d weight) εr (GHz) ratio (%) (ppm/° C.)  1 *0.137 0.137 0.363 0.363 0 39 67800 — 1.1  2 0.137 0.137 0.363 0.363 0.539 80600 18.9 2.1  3 * 0.136 0.138 0.361 0.365 0 38 64000 — 0.2  4 0.1360.138 0.361 0.365 0.5 38 75400 17.8 0.4  5 * 0.148 0.139 0.346 0.367 038 57600 — 4.8  6 0.148 0.139 0.346 0.367 0.5 38 67000 16.3 4.9  7 *0.142 0.139 0.364 0.355 0 38 63400 — −1.5  8 0.142 0.139 0.364 0.355 0.538 75400 18.9 −2.1  9 * 0.153 0.121 0.367 0.359 0 37 52400 — −5.7 100.153 0.121 0.367 0.359 0.5 37 60900 16.3 −5.3 11 * 0.143 0.147 0.3580.352 0 38 62500 — −3.8 12 0.143 0.147 0.358 0.352 0.5 38 77600 24.2−4.4 13 * 0.151 0.148 0.354 0.347 0 37 67800 — −7.2 14 0.151 0.148 0.3540.347 0.5 37 77700 14.6 −8.5 15 * 0.154 0.154 0.346 0.346 0 37 64600 —−10 16 0.154 0.154 0.346 0.346 0.5 37 76400 18.2 −9.4 17 * 0.139 0.1590.331 0.371 0 33 50500 — −1.4 18 0.139 0.159 0.331 0.371 0.5 33 5980018.4 −1.1 19 * 0.156 0.160 0.345 0.339 0 37 68200 — −11.8 20 0.156 0.1600.345 0.339 0.5 37 80100 17.4 −10.9 21 * 0.150 0.157 0.340 0.353 0 3464200 — −23.8 22 0.150 0.157 0.340 0.353 0.5 34 76300 18.9 −24.9 23 *0.162 0.165 0.337 0.336 0 36 70700 — −13.9 24 0.162 0.165 0.337 0.3360.5 36 84400 19.4 −14.7 25 * 0.165 0.168 0.330 0.337 0 35 69800 — −19.526 0.165 0.168 0.330 0.337 0.5 35 81900 17.4 −18.4 27 * 0.171 0.1710.329 0.329 0 33 62300 — −22.4 28 0.171 0.171 0.329 0.329 0.5 33 7370018.3 −23.4 29 * 0.161 0.161 0.355 0.323 0 36 53400 — −14.8 30 0.1610.161 0.355 0.323 0.5 36 65300 22.3 −15 31 * 0.172 0.168 0.330 0.330 031 62000 — −27.7 32 0.172 0.168 0.330 0.330 0.5 31 72400 16.7 −28.6 33 *0.141 0.161 0.322 0.376 0 33 48100 — −18.4 34 0.141 0.161 0.322 0.3760.5 33 57400 19.4 −17.3 35 * 0.132 0.142 0.366 0.360 0 40 65900 — 2.4 360.132 0.142 0.366 0.360 0.5 40 76600 16.2 3.3 37 * 0.129 0.129 0.3710.371 0 40 67800 — 5.1 38 0.129 0.129 0.371 0.371 0.5 40 80100 18.2 6.139 * 0.150 0.121 0.368 0.361 0 38 45300 — −6.2 40 0.150 0.121 0.3680.361 0.5 38 54000 19.2 −5.4

[0030] TABLE 2 Q × f Fe2O3 value- La2O3 Al2O3 SrO TiO2 (parts by Q × fincreasing τf Sample a b c d weight) εr (GHz) ratio (%) (ppm/° C.) 41 *0.125 0.128 0.380 0.367 0 41 62400 — 8.4 42 0.125 0.128 0.380 0.367 0.541 73400 17.6 8.5 43 * 0.122 0.119 0.382 0.377 0 42 57700 — 15.4 440.122 0.119 0.382 0.377 0.5 42 68500 18.8 15.9 45 * 0.117 0.152 0.3430.388 0 40 47400 — 5.1 46 0.117 0.152 0.343 0.388 0.5 40 56000 18.2 5.947 * 0.144 0.119 0.388 0.349 0 44 42300 — 10.2 48 0.144 0.119 0.3880.349 0.5 44 50300 18.9 10.9 49 * 0.113 0.113 0.387 0.387 0 44 49800 —24.3 50 0.113 0.113 0.387 0.387 0.5 44 59000 18.4 24.7 51 * 0.141 0.1180.345 0.396 0 38 41400 — 14.3 52 0.141 0.118 0.345 0.396 0.5 38 5070022.4 14.9 53 * 0.115 0.111 0.384 0.390 0 45 53500 — 27.1 54 0.115 0.1110.384 0.390 0.5 45 62400 16.7 26.4 55 * 0.107 0.119 0.384 0.390 0 4643200 — 35 56 * 0.159 0.179 0.331 0.331 0 29 58200 — −41 57 * 0.0850.085 0.415 0.415 0 57 40200 — 64 58 * 0.119 0.107 0.384 0.390 0 4836000 — 38 59 * 0.174 0.138 0.347 0.341 0 34 23600 — 15 60 * 0.117 0.1140.396 0.373 0 49 43200 — 38 61 * 0.194 0.194 0.306 0.306 0 27 53200 —−42 62 * 0.170 0.166 0.361 0.303 0 29 52700 — −34 63 * 0.170 0.166 0.3020.362 0 25 32200 — −18 64 * 0.117 0.114 0.371 0.398 0 52 37800 — 49

[0031] Hereinafter, the mixed powder was wet-mixed for 16 hours by meansof a ball mill. Then, water was removed therefrom, and the powder wasdried and calcined at a temperature of 1100 to 1200° C. for 3 hours.Thus, the calcined powder as the major component was produced.

[0032] Subsequently, 0.5 parts by weight based on 100 parts by weight ofthe major component of iron oxide (Fe₂O₃) as an Fe compound was added tothe calcined powder as shown in Tables 1 and 2. Then, an appropriateamount of a binder was added, and the powder was wet-crushed for 16hours by means of a ball mill. Thus, an adjusted powder was produced.

[0033] Thereafter, the adjusted powder was press-formed into a diskshape at a pressure of 1000 to 2000 kg/cm² and fired in the atmosphereat a temperature of 1500 to 1650° C. for 4 hours. Thus, a sintered piecehaving a diameter of 10 mm and a thickness of 5 mm was obtained.

[0034] The dielectric constant (er) and the Q value of the sinteredpiece were measured at a frequency (f) of 6 to 8 GHz by the both-endshortening type dielectric resonator method. The Q×f value wascalculated. The temperature coefficient (τ_(f), 25° C. to 55° C.) of theresonance frequency was measured based on the TE010δ mode resonancefrequency. Tables 1 and 2 show the results. It should be noted that inTables 1 and 2, the samples with sample-numbers having “star marks”depart from the scope of the present invention. The other samples arewithin the scope of the present invention.

[0035] As seen in Tables 1 and 2, in the case in which the majorcomponents having a composition formula of aRe₂O₃—bAl₂O₃—cSrO—dTiO₂ inwhich a, b, c, and d satisfy formulae of 0.113≦a≦0.172, 0.111≦b≦0.171,0.322≦c≦0.388, 0.323≦d≦0.396, and a+b+c+d=1.000 as in Samples 1 to 54,the sintered pieces have superior microwave dielectric characteristics.That is, the dielectric constants are high, i.e., at least 30, the Q×fvalues are high, i.e., at least 40,000 GHz, and the absolute values ofthe temperature coefficients (τf) of the resonance frequency are within30 ppm/° C., i.e., nearly zero.

[0036] On the other hand, in the case in which the compositions of themajor components departs from the above-described range as seen inSamples 55 to 64, undesirably, the dielectric constants (ε_(r)) are lessthan 30, the Q×f values are less than 40,000 GHz, or the temperaturecoefficients (τ_(f)) of the resonance frequencies exceeds 30 (ppm/° C.).

[0037] Then, as seen in Samples having even sample-numbers in the rangeof 1 to 54, by addition of 0.5 parts by weight on a Fe₂O₃ conversionbasis of Fe as an element, based on 100 parts by weight of a majorcomponent of which the composition formula is in the above-describedrange to exhibits a superior microwave dielectric characteristic, theQ×f values are significantly high compared to those of the majorcomponents of which the compositions are the same as those of theabove-described Samples except that no Fe₂O₃ is added (the sample havingan odd number which is smaller by 1 than each of the sample having theabove-mentioned even numbers). Thus, the Q value can be significantlyincreased by incorporating the Fe element into a Re₂O₃—Al₂O₃—SrO—TiO₂type composition.

Example 2

[0038] As starting materials, powders of La₂O₃ as a rare earth oxide(Re₂O₃), aluminum oxide (Al₂O₃), strontium carbonate (SrCO₃), andtitanium oxide (TiO₂) each having a high purity were prepared.

[0039] Subsequently, the raw materials were mixed so as to obtaincompositions having a composition formula of0.137La₂O₃—0.137Al₂O₃—0.363SrO—0.363TiO₂ (the coefficients are expressedby molar ratios). The composition was processed in a similar manner tothat for Example 1. Thus, the calcined powders as the major componentswere obtained. TABLE 3 Q × f Fe2O3 value- La2O3 Al2O3 SrO TiO2 (parts byQ × f increasing τf Sample a b c d weight) εr (GHz) ratio (%) (ppm/° C.)71 * 0.137 0.137 0.363 0.363 0 39 67800 — 1.1 72 0.137 0.137 0.363 0.3630.5 39 80600 18.9 2.1 73 0.137 0.137 0.363 0.363 0.01 39 73700 8.7 1.474 0.137 0.137 0.363 0.363 0.02 39 75600 11.5 1.7 75 0.137 0.137 0.3630.363 0.05 39 76700 13.2 1.6 76 0.137 0.137 0.363 0.363 1 39 79500 17.32.3 77 0.137 0.137 0.363 0.363 2 40 70900 4.5 2.5 78 * 0.137 0.137 0.3630.363 3 40 64100 −5.4 3.4 79 * 0.137 0.137 0.363 0.363 4 40 56100 −17.23.4

[0040] Subsequently, 0.01 to 4 parts by weight based on 100 parts byweight of the major component of iron oxide (Fe₂O₃) was added to thecalcined powder as shown in Table 3. Then, an appropriate amount of abinder was added. The powders were wet-crushed for 16 hours by means ofa ball mill. Thus, the adjusted powders were produced. Thereafter,sintered pieces were produced in a similar manner to that for Example 1.

[0041] For the produced sintered pieces, the dielectric constant (er),the Q×f value, and the temperature coefficient (τ_(f)) of the resonancefrequency were determined. Table 3 shows the results. In Table 3, thesamples having the sample numbers with star marks depart from the scopeof the present invention. All of the other samples are within the scopeof the present invention.

[0042] Referring to Table 3, as seen in Samples 72 to 77, the Q×f valuecan be enhanced by addition of 0.01 to 2 parts by weight of Fe₂O₃ basedon 100 parts by weight of the major component, as compared with the casein which Fe₂O₃ is not added. To the contrary, when the addition amountof Fe₂O₃ exceeds 2 parts by weight as in Samples 78 and 79, the Q×fvalue is decreased. Accordingly, the content on an Fe₂O₃ conversionbasis of Fe as an element is preferably in the range of 0.01 to 2 partsby weight based on 100 parts by weight of the major component.

Example 3

[0043] As starting materials, powders of La₂O₃, Nd₃O₃, Ce₂O₃, Pr₂O₃,Pm₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃,and Lu₂O₃, each having a high purity, were prepared. Moreover, powdersof aluminum oxide (Al₂O₃), strontium carbonate (SrCO₃), and titaniumoxide (TiO₂) were prepared.

[0044] Subsequently, these raw materials were mixed so as to obtain acomposition having a composition formula of0.137Re₂O₃—0.137Al₂O₃·0.363SrO—0.363TiO₂ (the coefficients are expressedby a molar ratio) in which the Re of Re₂O₃ is an element shown in Table4. The mixed materials were processed in a similar manner to that forExample 1 to obtain calcined powders as the major components. TABLE 4 Q× f Fe2O3 value- Re (parts by Q × f increasing τf Sample (Rare earthelement) weight) εr (GHz) ratio (%) (ppm/° C.)  81 * 0.8 La-0.2 Nd 0 3964300 — 1.3  82 0.8 La-0.2 Nd 0.5 39 73500 14.3 1.5  83 * 0.5 La-0.5 Nd0 38 62500 — 0.8  84 0.5 La-0.5 Nd 0.5 38 70400 12.7 1.5  85 * 0.2La-0.8 Nd 0 38 61000 — 0.5  86 0.2 La-0.8 Nd 0.5 38 69700 14.3 0.0  87 *0.8 La-0.2 Ce 0 39 59800 — 0.7  88 0.8 La-0.2 Ce 0.5 39 69800 16.7 0.9 89 * 0.8 La-0.2 Pr 0 39 62300 — 0.8  90 0.8 La-0.2 Pr 0.5 39 72100 15.81.2  91 * 0.8 La-0.2 Pm 0 39 61900 — 0.4  92 0.8 La-0.2 Pm 0.5 39 7080014.3 0.1  93 * 0.8 La-0.2 Sm 0 39 62700 — −0.2  94 0.8 La-0.2 Sm 0.5 3973700 17.6 0.3  95 * 0.8 La-0.2 Eu 0 39 52300 — 0.1  96 0.8 La-0.2 Eu0.5 39 60400 15.4 −0.2  97 * 0.8 La-0.2 Gd 0 38 57800 — −0.4  98 0.8La-0.2 Gd 0.5 38 64800 12.1 0.5  99 * 0.8 La-0.2 Tb 0 38 59800 — −0.7100 0.8 La-0.2 Tb 0.5 38 70700 18.2 −0.2 101 * 0.8 La-0.2 Dy 0 38 61500— −0.1 102 0.8 La-0.2 Dy 0.5 38 71300 16.0 0.7 103 * 0.8 La-0.2 Ho 0 3857800 — −0.9 104 0.8 La-0.2 Ho 0.5 38 67300 16.4 −1.1 105 * 0.8 La-0.2Er 0 38 57400 — −0.4 106 0.8 La-0.2 Er 0.5 38 67200 17.0 −0.7 107 * 0.8La-0.2 Tm 0 38 59100 — −0.8 108 0.8 La-0.2 Tm 0.5 38 68100 15.3 −0.3109 * 0.8 La-0.2 Yb 0 37 54300 — −1.3 110 0.8 La-0.2 Yb 0.5 37 6240014.9 0.1 111 * 0.8 La-0.2 Lu 0 37 56200 — −1.2 112 0.8 La-0.2 Lu 0.5 3763700 13.4 0.4 113 * 0.5 La-0.2 Nd-0.3 Ce 0 38 61300 — 0.2 114 0.5La-0.2 Nd-0.3 Ce 0.5 38 68900 12.4 1.1 115 * 0.2 La-0.4 Sm-0.4 Yb 0 3656900 — −1.7 116 0.2 La-0.4 Sm-0.4 Yb 0.5 36 67000 17.8 −0.2 117 * 0.3La-0.4 Eu-0.3 Dy 0 34 55700 — −2.8 118 0.3 La-0.4 Eu-0.3 Dy 0.5 34 6430015.4 −3.2

[0045] Thereafter, 0.5 parts by weight based on 100 parts by weight ofeach major component of iron oxide (Fe₂O₃) was added to the eachcalcined powder, and moreover, an appropriate amount of a binder wasadded as shown in Table 4. Then, the mixtures were wet-crushed for 16hours by means of a ball mill to obtain adjusted powders. The powderswere processed in a similar manner as that for Example 1 to producesintered pieces.

[0046] For the sintered pieces, the dielectric constant (ε_(r)), the Q×fvalue, and the temperature coefficient (Tr) of the resonance frequencywere determined. Table 4 shows these results. The samples havingsample-numbers with a star mark shown in Table 4 depart from the scopeof the present invention, and all of the other samples are within thescope of the present invention.

[0047] As seen in Table 4, for the sintered pieces each having a part ofLa substituted by another rare earth element, the Q×f value can be alsoenhanced by addition of Fe₂O₃ as seen in Samples having even numbers inthe range of 81 to 118, as compared to Samples having no Fe₂O₃ addedthereto (the Sample having the odd number which is smaller by 1 thaneach Sample having an even number).

[0048] In the above-described Examples, iron oxide (Fe₂O₃) is employedas the compound containing Fe as an element. Compounds containing Fe asan element such as iron oxides of FeO and Fe₃O₄, sulfates, chloride orthe life containing Fe as an element may be used. In this case, similaradvantages can be also obtained.

[0049] Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

What is claimed is:
 1. A high frequency dielectric ceramic compositioncomprising: a major component which contains a rare earth element (Re),Al, Sr, and Ti as metal elements, wherein a composition formula of themajor component is expressed by a molar ratio ofaRe₂O₃—bAl₂O₃—cSrO—dTiO₂ in which a, b, c, and d satisfy the followingformula; 0.113≦a≦0.172, 0.111≦b≦0.171, 0.322≦c≦0.388, 0.323≦d≦0.396, anda+b+c+d=1.000; and  a sub-component which contains 0.01 to 2 parts byweight of Fe as an element on the basis of Fe₂O₃, with respect to 100parts by weight of the major component.
 2. The high frequency dielectricceramic composition according to claim 1, wherein the rare earth element(Re) comprises La.
 3. The high frequency dielectric ceramic compositionaccording to claim 1, wherein the rare earth element (Re) comprises Laand at least one other rare earth elements.
 4. The high frequencydielectric ceramic composition according to claim 1, wherein thedielectric ceramic composition has a dielectric constant of at least 30.5. The high frequency dielectric ceramic composition according to claim1, wherein the dielectric ceramic composition has a Q×f value of atleast 40,000 GHz.
 6. The high frequency dielectric ceramic compositionaccording to claim 1, wherein an absolute value of a temperaturecoefficient of a resonant frequency of the dielectric ceramiccomposition is within 30 ppm/° C.
 7. The high frequency dielectricceramic composition according to claim 1, wherein the dielectric ceramiccomposition has a dielectric constant of at least 30, a Q×f value of atleast 40,000 GHz, and an absolute value of a temperature coefficient ofa resonant frequency within 30 ppm/° C.
 8. A dielectric resonator,comprising: a dielectric ceramic comprising: a major component whichcontains a rare earth element (Re), Al, Sr, and Ti as metal elements,wherein a composition formula of the major component is expressed by amolar ratio of aRe₂O₃—bAl₂O₃—cSrO—dTiO₂ in which a, b, c, and d satisfythe following formula; 0.113≦a≦0.172, 0.111≦b≦0.171, 0.322≦c≦0.388,0.323≦d≦0.396, and a+b+c+d=1.000; and  a sub-component which contains0.01 to 2 parts by weight of Fe as an element on the basis of Fe₂O₃,with respect to 100 parts by weight of the major component.
 9. Thedielectric resonator according to claim 8, further comprising a metalliccase within which the dielectric ceramic is arranged.
 10. The dielectricresonator according to claim 9, wherein the dielectric ceramic issupported by a support within the metallic case.
 11. The dielectricresonator according to claim 8, wherein the dielectric resonator is aTE01δ mode dielectric resonator.
 12. The dielectric resonator accordingto claim 8, wherein the dielectric ceramic includes a through-hole, aninner conductor formed in the through-hole, and an outer conductorformed on at least a portion of a periphery of the dielectric ceramic.13. The dielectric resonator according to claim 8, wherein thedielectric resonator is a TEM mode dielectric resonator.
 14. Thedielectric resonator according to claim 8, wherein the dielectricceramic has a dielectric constant of at least 30, a Q×f value of atleast 40,000 GHz, and an absolute value of a temperature coefficient ofa resonant frequency within 30 ppm/° C.
 15. The dielectric resonatoraccording to claim 8, wherein the rare earth element (Re) comprises La.16. The dielectric resonator according to claim 8, wherein the rareearth element (Re) comprises La and at least one other rare earthelements.
 17. A dielectric filter comprising the dielectric resonatordefined in claim 8 and an external coupling means coupled to thedielectric ceramic.
 18. The dielectric filter according to claim 17,wherein the external coupling means include an input terminal coupled tothe dielectric ceramic; and an output terminal coupled to the dielectricceramic.
 19. A dielectric duplexer comprising at least two dielectricfilters, input-output connecting means connected to the dielectricfilters, respectively, and an antenna-connecting means connected to bothof the dielectric filters, at least one of the dielectric filters beingthe dielectric filter defined in claim
 17. 20. A communication devicecomprising the dielectric duplexer defined in claim 19, a transmissioncircuit connected to at least one of the input-output connecting means,a reception circuit connected to a different one of the input-outputconnecting means that the transmission circuit is connected, and anantenna connected to the antenna-connecting means.